In a camera having a strobe, if the strobe is provided near the photographing:lens of the camera, i.e., if the optical axes of the strobe and the photographing lens are close to each other, a red-eye phenomenon will occur when photographing people. This red-eye phenomenon occurs because, before the flash is discharged, the ambient light is low and thus the pupil of the eye is dilated. When the flash is discharged, the pupil cannot constrict quickly enough, since the discharge time is very short. Consequently, light from the flash enters the pupil, is incident on the retina (having a red color as a result of the blood in the capillaries), and is reflected back towards the strobe. Since the pupil has not constricted enough, the reflected red light will be transmitted back to the camera and recorded on the film. The result is that the eyes of the person who was photographed appear to have large red pupils.
If the strobe is located far enough away from the photographing lens, the red-eye:phenomenon can be avoided or sufficiently reduced. However, since it is convenient to provide a strobe on a camera, it is difficult to prevent the red-eye phenomenon.
Further, since the strobe is provided on the camera in a fixed position, it is impossible to vary the angle of the light emitted by the flash unit on the subject to be photographed. Therefore the mood of the photograph cannot be changed, since the shadows must always remain in a fixed position relative to the camera.
Furthermore, if the object is far away from the camera, the strobe cannot cast enough light on the object to obtain a properly exposed photograph.